Carrier frequency system



July 23, 1940. J. L. ILLS 2209.272

' cmmmn mmqunncw svsmn Filed Oct. 5. 1936 INVENTCR JOHN L. HILLS.

By IX/ M ATTORNEYS Patented July 23, 1940 2,209,272 CARRIER FREQUENCY SYSTEM John Lionel Hills, Keston Park, England, assignor to The Fairey Aviation Company Limited, Hayes, Middlesex, England, a British com- Application October 5, 1936, Serial No. 104,134

In Great Britain October 10, 1935 6 Claims.

This invention relates to carrier frequency electric systems for communication, signalling, indicating, remote control and other purposes.

According to the present invention the frequency of a transmitter is caused during transmission to vary continuously over the whole or part of a predetermined frequency spectrum band of, say, 100 kilocycles and in any regular or irregular manner, and the local oscillations of a 1 heterodyne receiver for said transmitter are also caused to vary continuously over the whole or part of said frequency spectrum band but in a different manner. Thus, in one example the two frequencies may swing periodically to and fro across the predetermined spectrum band either at different respective periodicities, or mutually out of phase, or differently non-harmonically, the essential feature being that both frequencies are constantly changing and are never the same except when they may happen to cross each other or closely approach each other during their respective swingings toand fro within the spectrum band. In general the manner or law of frequency variation may be entirely irregular or 25 erratic or even fortuitous and the variation may be effected in a great many ways per se known in the art. It will be appreciated that the frequency variation over a spectrum band of say 100 kilocycles may when operating at short wave lengths of the order of, say, 10 metres, be achieved by relatively minute movements of a tuning element such as a trimming condenser or inductance for example. A more practical way for many purposes is to effect a positive cyclic variation such 3 as by employing a trimming condenser or even a main tuning condenser having a member or electrode which is continuously moved or oscillated or rotated such as by clockwork or a small electric motor or by a wind vane or propeller or even 40 through reduction gear from an engine which may be an aero-engine, said condenser member or electrode, which is conveniently moved cyclically or oscillated or rotated at a relatively slow periodicity of say 5 or 7 per second, may have 45 any desired shape or contour or profile so that the frequency swinging follows cyclically a definite law which may in fact be quite irregular but is conveniently simple. The law at. the receiver is preferably different from that at the transmitter in case the respective cycles might become in phase.

In the case of speech modulation of the wobbling carrier, the wobble rate should be at nonaudio frequency, such for example as 5 or 7 times per second, or it may be supersonic frequency.

The input circuit of the mixer or first detector of the receiver is preferably made substantially aperiodic with respect to the aforesaid frequency spectrum band whilst the intermediate frequency amplifier is made substantially aperiodic 5 with respect to the entire heterodyne frequency range derived from said first detector or mixer. As an example the transmitted frequency may be varied between 56,000 kilocycles and 56,100 kilocycles, in which case the intermediate frequency circuit may be broadly responsive to the corresponding frequency range of from 10 to 500 kilocycles. Thus, it will be appreciated, the transmitted speech or signals will be heard in spite of the constantly changing frequencies of both 15 the transmitted carrier and the'local oscillator of the receiver. In case the two swinging frequencies cross each other or.approach each other closely'there will be a brief interference .which however is of no consequence for many 0 purposes of the invention, such as for speech between aircraft or for military purposes or the like. The effects of such interference can be minimised in various ways such as by known frequency discriminating devices. Thus there may be provided a rejector circuit for frequencies up to 10,000 in a manner which has been common knowledge for many years. It would in fact in practice he diflicult to design a pass circuit for this range which would pass also frequencies from 30 10500 kilocycles as will be clear to anyone skilled in the art.

It will be appreciated that a receiver as above set forth may receive simultaneously and. without appreciable interference or jamming transmissions from several transmitters as above set forth assuming, of course, that the transmitters are not actually speaking simultaneously. The invention thus provides, according to an important feature of the invention, a satisfactory conference communication system wherein several stations can join in a conversation without the switching or duplication of apparatus or other complication as has heretofore been necessary.

According to an important feature of the invention, the local oscillations at each station are the oscillations transmitted from that station, that is to say the local receiver receives to advantage both the local carrier and the distant carrier, so that considerable simplification of plant is obtained.

Although the invention has been hereinbefore mainly set forth as for radio telephonic communication, it is to be fully understood that it is in no way limited to such application since obviously the output of the receiver may be applied to devices otherthan or in additionto sound reproducers, namely, to meters and other forms of indicators whereby the presence of transmitters having similar apparatus may be detected or indicated such as in fog or darkness, and furthermore such indicators may be made selective such as to frequency and/or amplitude and/or polarisation and by employing directional aerials, goniometers or the like, bearings may be obtained and aeroplanes and other travelling objects may be located as to direction and be guided by radio beacon effect. The invention is applicable also to the remote or automatic control of numerous forms of apparatus..

To enable the invention to be clearly understood it will now be described by way of example with reference to the accompanying drawing in which the single figure is a purely diagrammatic representation of the main devices and their connections of a complete systemin accordance with the invention.

In the accompanying drawing at T is shown by a rectangle the short-wave transmitter, the carrier frequency of which is caused to vary cyclically as hereinbefore set forth, by the continued rotation at say 5 or '7 revolutions per second of a moving plate or plates of a tuning condenser I, which for the purpose of simple example and illustration has similar oval or elliptical plates, the moving plate or plates being rotated by an electric or clockwork or other motor 2 through a gear box 3. Instead of such arrangement, it will be understood that many other arrangements may be alternatively employed for cyclically varying the transmitted frequency.

At 4 is shown a microphone, but it will be appreciated that the carrier wave may be modulated otherwise than by means of speech. The transmitter aerial is shown at 5, which aerial may be of any known or convenient type.

Adjacent the transmitter T is the receiver having a receiving aerial 6. The aerial 6 is connected to the mixer or frequency changer or first detector DI, the output of which is connected to the intermediate frequency amplifier IFA and the output of the latter is connected to the second detector D2. The output of the second detector D2 is shown connected to headphones P and there are also shown by way of example switches S2 and S3, whereby the output of the second detector D2, which of course may be followed by a low frequency amplifier (not shown), may be applied to other devices, namely, by the switch S2 to a relay Ri which may control the operation or effect a change in the condition of any desired form of apparatus indicated in the drawing by the rectangle B. The relay RI may be actuated by the voltage developed in a tuned circuit Cl which may be made resonant as desired to a particular audio frequency. The switch S3 is supposed to connect the output of the detector D2 to a meter or indicator Ma such as a milliammeter and if for example this meter or indicator is required to the selective to the modulation amplitude of the transmitted waves a rectifier 1 may be included in the circuit.

It will be appreciated thatthe aerial circuit 6 and the intermediate frequency amplifier IFA are selective to the entire intermediate frequency range (less the range from 0-10,000 cycles per second) due on the one hand to the varying frequency of the waves transmitted from the distant station and on the other hand to the varying frequency of the illustrated local transmitter T which is acting as the local oscillator for the mixer DI. The requisite broad pass characteristic of the intermediate frequency amplifier IF'A may be conveniently obtained in known manner by the employment of resistance-capacity intervalve couplings with appropriate values of resistance and capacity.

It is to be understood that the invention is in no way limited to the arrangements herelnbefore specifically described with reference to the drawing and that it has numerous other applications than radio telephones.

I claim:

1. The method of carrier frequency communication, which consists in transmitting a carrier, continuously varying the frequency of said carrier within the limits of a predetermined frequency spectrum band of more than 10 kilocycles, impressing signal currents on said carrier, receiving the varying frequency carrier at a remote receiver and there supersonically heterodyning it by local oscillations, varying the frequency of said local oscillations continuously but differently and not at constant phase difference also within the limits of said spectrum band, P ssing the whole of the resultant varying intermediate frequency through the intermediate frequency circuit which accepts substantially aperiodically all the heterodyne difference frequencies from near zero up to a maximum frequency which is equal to the difference between the upper and lower limits of the aforesaid spectrum band and which rejects higher frequencies, and effecting secondary detection of said resultant intermediate frequency so as to derive only said signal currents from said resultant intermediate frequency.

2. The method of conference typecarrier frequency inter-communication, which consists in transmitting simultaneously from at least 3 transmitter-receiver stations respective carriers the frequencies of all of which are continuously but differently varying within the limits of a predetermined frequency spectrum band, modulating said carriers mainly at different times causing at least one of said stations to receive at least two of the transmitted carriers of varying frequency and utilizing the local transmitter carrier of varying frequency aforesaid to heterodyne supersonically the received carriers, passing the whole of the resultant varying intermediate frequency through a circuit substantially aperiodic thereto, and effecting secondary detection thereof so as to derive the modulation of at least one other station.

3. The method of conference type carrier frequency communication, which consists in transmitting simultaneously from a plurality of transmitter-receiver stations respective carriers, the frequencies of all of which are caused to vary continuously but differently within the limits of a single predetermined frequency spectrum band, modulating said carriers mainly at different times causing at least one of said stations to receive at least one ofthe transmitted carriers of varying frequency while heterodyning it supersonically and at continuously varying frequency as aforesaid, passing the whole of the resultant varying intermediate frequency through a circuit substantially aperiodic thereto, effecting secondary detection thereof and effecting minimization of audio-frequency heterodyne interference effects which necessarily tend to occur at intervals.

.A. carrier frequency system, comprising a transmitter means for modulating the carrier transmitted therefrom, a superheterodyne receiver, independent means for varying continuousiy but differently both the transmitted carrier frequency and the frequency of the local oscillations of said superheterodyne receiver within the limits of a single predetermined frequency spectrum band, of more than- 10 kilocycles, the intermediate frequency circuit of the receiver accepting substantially aperiodically all the heterodyne difference frequencies from near zero up to a maximum frequency which is equal to the difference between the upper and lower limits of the aforesaidspectrum band and rejecting higher frequencies, and a second detector for deriving only the transmitted carrier modulation from said varying intermediate frequency.

5. A carrier frequency station comprising in combination a carrier wave transmitter means for modulating the carrier transmitted therefrom, means for continuously varying the carrier frequency within the limits of a predetermined frequency spectrum band of more than 10 kilocycles, and associated with said transmitter as part of the station a superheterodyne receiver having an intermediate frequency circuit accepting substantially aperiodically to the entire intermediate different frequency range from near zero up to a maximum frequency equal to the difference between the limits of said spectrum band due to the whole frequency variation of said adjacent transmitter acting as local oscillator adapted to heterodyne another modulated received carrier the frequency of-which also varies within the limits of the same frequency spectrum band and a second detector for deriving only the transmitted carrier modulation from said varying intermediate frequency.

6. A carrier frequency station as claimed in claim 5, wherein means is provided for excepting the audio-frequency range from the aperiodically acceptedrange.

JOHN mom HILLS. 

